At least 30 people, and possibly dozens more, were killed in Syria on Thursday in the northern Raqqa province, when government warplanes bombed a gas station crowded with cars and people, according to a witness at the scene and activist groups.

One man who witnessed the aftermath said the gas station was on the outskirts of the town of Ayn Issa, near a border post with Turkey that Syrian opposition fighters had stormed two days ago. The Syrian Observatory for Human Rights, a group based in Britain with a network of contacts in Syria, said 110 people were either killed or wounded.

If verified, the bombing would be one of the worst casualty tolls from the Syrian military's use of aircraft in its effort to crush the insurgency. Stretched thin by a persistent, far-flung rebellion, and facing greater challenges from improvised bombs on Syria's roads, the military has increasingly relied on warplanes and helicopters to extend its reach.

On Thursday, one of those helicopters crashed in a suburb of Damascus that has been the site of persistent fighting between rebels and government forces, according to Syrian officials.

The official Syrian news agency said the helicopter's rotors had clipped the tail of a Syrian Air passenger jet with 200 people aboard. It said the jet had landed safely at the Damascus airport and no one had been injured. But an activist in Damascus said a rebel battalion shot down the helicopter, which crashed near the town of Douma.

It was unclear whether anyone aboard the helicopter as killed or injured.

While rebels claim to have brought down planes in the past, the authorities routinely blame such crashes on mechanical failures.

At the gas station near the Turkish border, an activist who went to the scene said that the station, called the Hisham station, had been crowded with cars when the bombs were dropped. He said the warplanes dropped barrel bombs, an improvised government weapon filled with TNT that opposition fighters have claimed the military is deploying with greater frequency.

Videos that were said to be of the gas station after the bombing showed at least two shallow craters in the ground, encircled by a ring of destruction, including smoldering trucks with their doors flung open, and a burned-out tractor.